1. Field of the Invention
The present invention relates to a flexible press cover which is intended for a shoe press roll.
2. Description of the Related Art
A shoe press roll of this type is used for dewatering or calendering a moving fibrous web, in particular a paper or board web. The flexible press cover includes a plastic layer, preferably made of polyurethane and, as a strengthening element, a (“conventional”) reinforcement embedded in the plastic layer. The reinforcement can be formed as a woven fabric; however, preference is given to what is known as a laid fabric, which includes axially parallel longitudinal filaments and circumferential filaments wound in. The circumferential filaments can be wound into the plastic layer on the outer side of the longitudinal filaments (see EP 0330680=U.S. Pat. No. 5,134,010, PH 04378). However, the opposite arrangement is likewise possible (see WO 95/29293, Tamfelt).
In relation to the prior art, reference is made to the following further documents:    D1: DE 3546650 C2, (PH 04164A),    D2: DE 29702362, (PH 10287),    D3: DE 19633543 (PH 10368).
As is known, a shoe press roll includes a stationary supporting element. Rotatably mounted on the latter are two cover carrying disks for the flexible press cover. In addition, there is arranged on the supporting element a radially displaceable press shoe, which is able to press the revolving press cover against an opposing roll in order to form a press nip extended in the web running direction. It is important that the press cover and the cover carrying disks, together with the supporting element, bound a closed, liquid-tight internal space.
According to document D1, in order to achieve a liquid-tight connection between the press cover end region and one of the cover carrying disks, provision is made to bend over the end region radially inward and to press it against the outer end of the cover carrying disk with the aid of clamping elements.
This arrangement has been tried and tested in practice. However, it is disadvantageous in that a large number of recesses has to be provided in the edge zone of the press cover, between which recesses tongues remain. In some cases, difficulties also arise in achieving the most exact circularity of the press cover.
According to FIGS. 3 and 4 of document D2, attempts have been made to avoid the deformation of the press cover end region described in D1. Each of the two press cover end regions retains the normal cylindrical form, so that the production of recesses and tongues is dispensed with. Provision is made to clamp the cylindrical press cover end region in between an internal expandable (that is to say of enlargeable diameter) spreader ring and an outer ring. However, such an outer ring is frequently disruptive, since the replacement of a worn press cover by a new press cover is more awkward.
According to FIGS. 2 to 4 of document D3, an annular circumferential groove is provided in the outer circumferential surface of a cover carrying disk, into which groove the annular region of the press cover is pressed, specifically by way of a clamping band or by way of a plurality of turns of a high-strength filament or by way of a shrinkage ring. If a covering provided in accordance with FIG. 1 at document D3 is left out, then there is no disruptive outer ring. Nevertheless, this known solution has not been able to gain acceptance in practice.
What is needed in the art is a flexible press cover where the production of recesses and tongues in the press cover end region is superfluous, the mounting of the press cover end region on the respective cover carrying disk is easily achievable, the mounted press cover has good circularity and the outer circumferential surface of the press cover is free of fixing elements.